In the field of motion tracking (also known as position tracking, position and orientation tracking, or pose tracking), six types of sensors are commonly employed: mechanical, acoustic, optical, magnetic, inertial, and radio-frequency (RF) sensors. Mechanical systems are generally avoided due to encumbrance of the person or object being tracked. For indoor precision applications, RF is generally not suitable due to coarse resolution and/or multipath interference. Similarly, use of magnetic systems has been declining due to difficulties with magnetic field distortion around metallic objects, and limited range. Motion tracking systems can be based on optical and/or acoustic sensors, which can also be used in combination with inertial sensors.
In acoustic tracking systems, the fundamental measurement can be a 1-degree of freedom (DOF) time-of-flight range measurement between an emitter and a receiver. The tracking system can determine object position by using multi-lateration of three or more range measurements between a single emitter (receiver) and multiple receivers (emitters).
In optical tracking systems, the fundamental measurement can be a 2-DOF bearing-angle measurement from a camera to a target (e.g., a light emitting diode (LED), reflector, marker, or object feature). To determine an object position in an “outside-in” system, two or more such bearing-angle measurements from separated cameras are combined with triangulation. In an “inside-out” system, one camera can observe four or more separated targets, which are used to solve a perspective-n-point (PnP) pose recovery algorithm.